Electrical pulse generating apparatus



June 17, 1969 I. E. LINKROUM 3,450,940

ELECTRICAL PULSE GENERATING APPARATUS Filed Aug. 29, 1967 N 117 C m mRECTIFIER INVENTOR. IRVING E. LINKROUM 5; mmfzf nm ATTOR EYS 3,450,940ELECTRICAL PULSE GENERATING APPARATUS Irving E. Linkrourn, Hancock,N.Y., assignor to The Bendix Corporation, a corporation of DelawareFiled Aug. 29, 1967, Ser. No. 664,171 Int. Cl. H05b 41/00 US. Cl.315-171 Claims ABSTRACT OF THE DISCLOSURE This invention relates toelectrical apparatus and more particularly to electrical pulsegenerating systems, such as ignition spark generating systems forcombustion engines and the like.

One of the objects of the present invention is to provide novelelectrical circuitry for generating simultaneous spark discharges at twoseries connected spark gaps.

Another object is to provide a novel combination of high and low energypulse generating circuits for alternatively firing a common ignitiongap.

A further object is to provide a simplified, highly efficient ignitionsystem which is novelly so constructed as to increase the normaloperating life of the components which are most likely to fail.

Still another object is to provide a spark generating system forcombustion engines comprising a novel series dual high energy startingcircuit in novel combination with a lower energy continuous dutycircuit.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration only and is not intended as a definition of the limits ofthe invention.

In the drawing, the single figure is a schematic diagram of one form ofelectrical circuit embodying the invention.

The single embodiment of the invention illustrated in the drawing by wayof example is in the form of an untimed ignition system for jet or gasturbine type engines. In these engines one level of spark energy isrequired to be supplied, preferably to a pair of ignition plugs, forstarting the engine, but a lower level of spark energy is adequate toenable one igniter plug to perform its functions as required whencontinuous operation of the engine is desired. This mode of operation ofthe ignition system results in a longer operating life for the igniterplugs and other components of the system. The illustrated systemaccordingly comprises a first starting circuit 5 for supplyingrelatively high energy, say 2 joules or more, at each of two seriesconnected igniter gaps and a second continuous duty circuit 6 novellyassociated with the first circuit for supplying a lower energy, say 0.5joule, to one of the igniter gaps. These circuits may be alternativelyenergized at the option of an operator or pilot by any suitable sourceof alternating or interrupted direct current, such as by a 115 volt 400cycle A.C. generator.

In the high energy circuit 5 when switch 7 is closed, a

nited States Patent 0 relatively large storage capacitor 8 is connectedto be charged, step by step, to some preselected voltage, say 2,000volts, through a transformer 9 and a suitable rectifier 10 in a knownmanner. A small storage and triggering capacitor 11 is connected acrosscapacitor 8 in series with a resistor 12 and the primary winding 14 of ahigh frequency transformer 13 through leads 15 and 16. Capacitor 11 willaccordingly be charged at the same time and to the same voltage ascapacitor 8. When switch 7 is open and switch 17 is closed, a storagecapacitor 18, which is smaller than capacitor 8, is connected to becharged in a similar fashion through a transformer 19 and a rectifier 20to a preselected voltage, say 2500 volts. These capacitors when thuscharged constitute sources of pulse energy to be supplied to a pair ofigniter gaps or plugs 21 and 22 which may be of the so-called lowtension shunted-surface gap type.

When the high energy circuit is in operation for energizing both igniterplugs 21 and 22 for starting the engine, the discharging of capacitor 8is in part controlled or triggered by a sealed control gap 23 having apredetermined spark-over or on-set voltage of say 2000 volts. Gap 23 isconnected across capacitor 8 in series with a small capacitor 24 and aprimary winding 25 of a high frequency transformer 26 through leads 27,28 and 16. Whenever the charge on capacitor 8 reaches the spark-overvoltage of control gap 23, it will discharge a small part of its chargeacross the gap through primary winding 25 into the small condenser 24.This discharge pulse will induce a high voltage pulse in the secondarywinding 29 of transformer 26 which is connected at one end to theungrounded terminal of igniter gap 22 and at its other end to the lowvoltage terminal of capacitor 8. The voltage is stepped up sufiicientlyby transformers 25, 29 to ionize igniter gap 22. The ionizing circuit iscompleted through ground and a small capacitor 30 which may be theinherent capacitance of the line or circuit components to ground.

Similarly and at the same time, upon breakdown or conduction of controlgap 23, as explained above, capacitor 11 will discharge through saidgapacross primary winding 14 to thereby induce a high voltage pulse insecondary winding 31 of high frequency step-up transformer 13. One endof winding 31 is connected to the un grounded terminal of igniter gap21. The other end of winding 31 is connected to the high potentialterminal of capacitor 8 through a control gap 32 having a spark-overvoltage, say 4000 volts, considerably in excess of the spark-overvoltage of control gap 23. The induced voltage in winding 31 is ofsufficient magnitude to bridge gap 32 and ionize igniter gap 21. Thebridging and ionizing circuit is completed through ground and a smallcapacitor 33 which may be the inherent capacitance of the line orcircuit components to ground. To better insure the breakdown of gap 32by the short low energy pulse in secondary winding 31, it is desirableto mount gaps 23 and 32 in a manner such that light from gap 23 when itfires will fall upon gap 32 and speed up the breakdown thereof.

With control gap 32 conductive and both igniter gaps 21 and 22 ionizedin the manner described above, high energy storage condenser 8 willdischarge across and produce high energy sparks at the igniter gaps vialead 27, gap 32, secondary windings 31 and 29, and lead 16. In the eventigniter plugs 21 fails to conduct for any reason, the discharge ofcondenser 8 proceeds via an inductor 34 and ground to igniter plug 22.If, on the other hand, plug 22 fails to conduct, the condenser dischargewill proceed from igniter plug 21 via ground and an inductor 35 to lead16. The parameters of the circuit components are such that inductors 34and 35 will delay appreciable conduction therethrough until igniter gaps21 and 22, respec- 3 tively, break down if the latter are functioningproperly.

Once the engine is started by high energy sparks resulting from thedischarge of capacitor 8 in the above manner, switch 7 is opened tode-energize the high energy circuit and switch 17 is closed to energizethe continuous duty low energy circuit 6 wherein the discharging ofstorage condenser 18 is controlled by a sealed gap 36 having apreselected breakdown or on-set voltage, say 2500 volts, somewhat inexcess of the breakdown voltage of gap 23. One terminal of gap 36 isconnected to the high potential side of capacitor 18, and the outputterminal thereof is connected through a lead 37 to ground and hence, tothe low potential terminal of capacitor 18 through parallel paths, oneof which comprises a primary winding 38 of transformer 26, a resistor 39and a small condenser 40 connected in series, and the other of whichcomprises secondary winding 29 of transformer 26 and igniter gap 22.

Whenever the charge on capacitor 18 attains the breakdown voltage ofcontrol gap 36, the latter is rendered conductive, and there results aninitial discharge of the capacitor through primary winding 38 andresistance 39 to capacitor 40. This pulse induces a high voltage pulsein secondary winding 29 which is effective to ionize igniter gap 22 andrender the same conductive to the discharge of capacitor 18 and hence,create a relatively low energy spark in the engine combustion chamber.The resistance 39 clamps and shortens the condenser discharge pulsethrough primary winding 38 to thereby avoid sufficient build-up ofvoltage in primary winding to fire igniter plug 21 through transformer13. The triggered spark gap arrangement in the high energy circuit 5prevents the low energy circuit 6 from firing back into the high energysystem through transformer 26.

The operations of the high and low energy circuits 5 and 6 as describedabove are repetitive and generate a succession of sparks at the igniterplugs. The sparking rate may be controlled by the circuit parameters andthe magnitude of the source voltage. By way of example, in some enginesthe spark rate requirement may range from one to five sparks per second.

In one successful jet engine ignition system embodying the invention,wherein the source voltage varied from 100 to 125 volts and thebreakdown or spark-over voltages of the control gaps were of themagnitudes suggested above, other basic components had the valuesindicated below:

Capacitor 8 7 microfarads. Capacitor 18 0.8 microfarad. Capacitors 11and 24 0.2 microfarad. Capacitor 40 0.02 microfarad. Resistance 12 50Kohms. Resistance 39 5 ohms. Inductors 34 and 35 80 turns #19. Primarywindings 14, 25 and 38 3 turns #17. Secondary windings 29 and 31 turns#17.

It will be noted that the on-set voltage (4000 v.) of gap 32 issufficiently high to prevent any flow of energy through igniter plug 21when the 2500 v. system 6 is in operation to fire plug 22. Additionally,the initial discharge of capacitor 18 through primary 38 into the smallcapacitor 40 is of high frequency and short duration and hence, theinduced voltage in secondary 29 is incapable of triggering gap 32, as isalso the induced voltage in primary 25. The latter is also insufiicientto charge capacitor 11 to the on-set voltage of gap 23. Similarly, suchtriggering of gap 32 cannot be effected by the subsequent 2500 v.discharge through winding 29 from capacitance 18. When the high energycircuit 5 is operating under control of the 2000 v. gap 23 the voltageinduced in winding 38 is less than 2000 v. and hence, insufficient tofire across the 2500 v. gap 36. In addition to the foregoing advantageswhich result in part from the use of a triggering gap system in the highenergy circuit, the oper- 4 ating life of gap 32 which carries the highenergy discharge of capacitor 8 is materially enhanced by the fact thatthe repetitive breakdown thereof is effected by lowenergy, high-voltagepulses from transformer 13.

Although only a single embodiment of the invention has been illustratedin the drawing and described in the foregoing specification, it will beunderstood that the same is not thus limited. For example, high tensionigniter plugs could be used in lieu of the low voltage plugs illustratedand inductors 35 and 36 could be replaced by suitable gaps. Variousother changes, particularly in the exemplary component values suggestedand in the arrangement of components illustrated may also be madewithout departing from the spirit and scope of the invention as the samewill now be understood by those skilled in the art.

What is claimed is:

1. An electrical pulse generating system comprising a first storagecapacitor, a second storage capacitor, means for simultaneously chargingsaid capacitors to a predetermined voltage, a step-up transformercomprising a primary and secondary windings, first control means forinitiating the discharge of said second capacitor through said primarywinding, a load circuit connected across said first storage capacitorand comprising said secondary winding and second control meansresponsive to the voltage induced in said secondary winding forinitiating discharge of said first capacitor through said load circuit.

2. An electrical pulse generating system as defined in claim 1 whereinsaid capacitors are connected in parallel circuits to a common source ofelectrical energy.

3. An electrical pulse generating system as defined in claim 2 whereinsaid source charges the capacitors stepby-step to the predeterminedvoltage.

4. An electrical pulse generating system as defined in claim 1 whereinsaid first control means is a triggering gap having a flash-over voltagesubstantially equal to said predetermined voltage.

5. An electrical pulse generating system as defined in claim 4 whereinsaid second control means is a control gap having a flash-over voltagein excess of the flash-over voltage of said triggering gap.

6. An electrical pulse generating system as defined in claim 1 whereinsaid load circuit includes an igniter plug.

7. An electrical pulse generating system as defined in claim 6comprising a second transformer having primary and secondary windings, athird capacitor connected in series with said last-named primary windingand said first control means across said first capacitor, and a secondigniter plug, the latter and the secondary winding ofsaid secondtransformer being connected in series with said first-named igniter plugand said second control means in said load circuit.

8. Electrical spark generating apparatus comprising a first storagecapacitor, a voltage step-up transformer having primary and secondarywindings, a second storage capacitor connected in series with saidprimary winding across said first capacitor, a triggering gap having apredetermined breakdown voltage connected in shunt across said primarywinding and said second capacitor, a load circuit comprising an ignitergap, a control gap connected in series with said secondary windingacross said first capacitor, said control gap having a breakdown voltagein excess of said predetermined voltage, means for repetitively chargingsaid capacitors simultaneously to said predetermined voltage, wherebysaid triggering gap is rendered conductive to the discharge of saidsecond capacitor through said primary winding to thereby induce asufiicient voltage across said secondary winding to render said controlgap and igniter gap conductive to the discharge of said first capacitor.

9. Electrical spark generating apparatus as defined in claim 8comprising a resistor connected in series with said second capacitor andsaid primary winding.

10. Electrical spark generating apparatus as defined in claim 8comprising a second transformer having primary and secondary windings, athird capacitor connected in series with said primary winding of thesecond transformer and said triggering gap across said first capacitor,and a second igniter gap and said secondary winding of the secondtransformer connected in series with said first-named igniter gap andsaid control gap in said load circuit.

11. Electrical spark generating apparatus as defined in claim 10comprising an inductor connected in shunt with a portion of the loadcircuit including said firstnamed igniter gap.

12. Electrical spark generating apparatus as defined in claim 11comprising an inductor connected in shunt with a portion of said loadcircuit including said second igniter gap.

13. Electrical spark generating apparatus as defined in claim 10comprising a fourth capacitor, a second control gap having a breakdownvoltage below that of said first-named control gap and above that ofsaid triggering gap, means for repetitively charging said fourthcapacitor to the breakdown voltage of said second control gap, a secondprimary winding inductively coupled with the secondary winding of saidsecond transformer and a fifth capacitor, said second control gap, saidsecond primary winding and said fifth capacitor being connected inseries across said fourth capacitor and said second control gap, saidsecondary winding of the second transformer and said second igniter gapbeing connected in series across said fourth capacitor.

14. Electrical spark generating apparatus as defined in claim 13comprising a resistor connected in series with said fifth capacitor.

15. Electrical spark generating apparatus as defined in claim 13comprising means for selectively connecting said first capacitor andsaid fourth capacitor to their respective charging means.

References Cited UNITED STATES PATENTS 3/1964 Collins 3l5209 X 6/1967Segall et al. 315-209 JOHN W. HUCKERT, Primary Examiner. R. F.POLISSACK, Assistant Examiner.

